I think it is a cherimoya, atemoyas have a more pronounced horn, and these look very smooth. I can tell you that it is not a Lisa or gefner atemoya, although it might be another variety, I am pretty sure it's a cherimoya.
I have little experience with cherimoya so I can't tell you the variety, bu if it tastes good then it doesn't mater too much.

I agree its Cherimoya without any doubt.